[media] media: Entity use count
Due to the wide differences between drivers regarding power management needs, the media controller does not implement power management. However, the media_entity structure includes a use_count field that media drivers can use to track the number of users of every entity for power management needs. The use_count field is owned by media drivers and must not be touched by entity drivers. Access to the field must be protected by the media device graph_mutex lock. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Acked-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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@ -258,3 +258,16 @@ When the graph traversal is complete the function will return NULL.
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Graph traversal can be interrupted at any moment. No cleanup function call is
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required and the graph structure can be freed normally.
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Use count and power handling
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----------------------------
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Due to the wide differences between drivers regarding power management needs,
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the media controller does not implement power management. However, the
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media_entity structure includes a use_count field that media drivers can use to
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track the number of users of every entity for power management needs.
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The use_count field is owned by media drivers and must not be touched by entity
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drivers. Access to the field must be protected by the media device graph_mutex
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lock.
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@ -73,6 +73,7 @@ int __must_check media_device_register(struct media_device *mdev)
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mdev->entity_id = 1;
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INIT_LIST_HEAD(&mdev->entities);
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spin_lock_init(&mdev->lock);
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mutex_init(&mdev->graph_mutex);
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/* Register the device node. */
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mdev->devnode.fops = &media_device_fops;
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@ -23,6 +23,7 @@
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <media/media-entity.h>
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#include <media/media-device.h>
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/**
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* media_entity_init - Initialize a media entity
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@ -195,6 +196,51 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
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}
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EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
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/* -----------------------------------------------------------------------------
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* Module use count
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*/
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/*
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* media_entity_get - Get a reference to the parent module
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* @entity: The entity
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*
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* Get a reference to the parent media device module.
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*
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* The function will return immediately if @entity is NULL.
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*
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* Return a pointer to the entity on success or NULL on failure.
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*/
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struct media_entity *media_entity_get(struct media_entity *entity)
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{
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if (entity == NULL)
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return NULL;
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if (entity->parent->dev &&
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!try_module_get(entity->parent->dev->driver->owner))
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return NULL;
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return entity;
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}
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EXPORT_SYMBOL_GPL(media_entity_get);
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/*
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* media_entity_put - Release the reference to the parent module
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* @entity: The entity
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*
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* Release the reference count acquired by media_entity_get().
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*
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* The function will return immediately if @entity is NULL.
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*/
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void media_entity_put(struct media_entity *entity)
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{
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if (entity == NULL)
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return;
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if (entity->parent->dev)
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module_put(entity->parent->dev->driver->owner);
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}
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EXPORT_SYMBOL_GPL(media_entity_put);
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/* -----------------------------------------------------------------------------
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* Links management
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*/
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@ -25,6 +25,7 @@
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#include <linux/device.h>
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#include <linux/list.h>
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#include <linux/mutex.h>
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#include <linux/spinlock.h>
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#include <media/media-devnode.h>
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@ -42,6 +43,7 @@
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* @entity_id: ID of the next entity to be registered
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* @entities: List of registered entities
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* @lock: Entities list lock
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* @graph_mutex: Entities graph operation lock
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*
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* This structure represents an abstract high-level media device. It allows easy
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* access to entities and provides basic media device-level support. The
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@ -69,6 +71,8 @@ struct media_device {
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/* Protects the entities list */
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spinlock_t lock;
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/* Serializes graph operations. */
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struct mutex graph_mutex;
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};
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/* media_devnode to media_device */
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@ -81,6 +81,12 @@ struct media_entity {
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struct media_pad *pads; /* Pads array (num_pads elements) */
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struct media_link *links; /* Links array (max_links elements)*/
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/* Reference counts must never be negative, but are signed integers on
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* purpose: a simple WARN_ON(<0) check can be used to detect reference
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* count bugs that would make them negative.
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*/
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int use_count; /* Use count for the entity. */
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union {
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/* Node specifications */
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struct {
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@ -129,6 +135,9 @@ void media_entity_cleanup(struct media_entity *entity);
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int media_entity_create_link(struct media_entity *source, u16 source_pad,
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struct media_entity *sink, u16 sink_pad, u32 flags);
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struct media_entity *media_entity_get(struct media_entity *entity);
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void media_entity_put(struct media_entity *entity);
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void media_entity_graph_walk_start(struct media_entity_graph *graph,
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struct media_entity *entity);
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struct media_entity *
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